The present invention relates generally to micro-electromechanical devices and, more particularly, to micro-electromechanical thermal actuators such as the type used in ink jet print heads.
Micro-electro mechanical systems (MEMS) are a relatively recent development. Such MEMS are being used as alternatives to conventional electromechanical devices such as actuators, valves, and positioners. Micro-electro mechanical devices are potentially low cost, due to the use of microelectronic fabrication techniques. Novel applications are also being discovered due to the small size scale of MEMS devices.
Many potential applications of MEMS technology utilize thermal actuation to provide the motion needed in such devices. For example many actuators, valves, and positioners use thermal actuators for movement. In the design of thermal actuators it is desirable to maximize the degree of movement while also maximizing the degree of force supplied by the actuator upon activation. At the same time it is also desirable to minimize the power consumed by the actuator motion.
It is also advantageous that the cantilever type thermal actuator exhibits no change in intrinsic stress and repeatable actuator motion upon repeated thermal actuation of the actuator between 20xc2x0 C. and 300xc2x0 C. temperatures. It is also desirable that the resulting MEMS devices are capable of being produced in batch fashion using materials that are compatible with standard CMOS integrated circuit fabrication. This allows advantageous MEMS devices that are reliable, repeatable, and low in cost. Compatibility with CMOS processing also allows the integration of control circuitry with the actuator on the same device, further improving cost and reliability.
It is therefore an object of the present invention to provide a thermal actuator for a micromechanical device having an actuator beam with an improved degree of movement.
It is a further object of the present invention to provide a thermal actuator for a micromechanical device having an actuator beam that delivers an increased degree of force upon activation.
Yet another object of the present invention is to provide a cantilevered beam type thermal actuator that exhibits substantially no relaxation upon repeated thermal actuation of the actuator between 20xc2x0 C. and 300xc2x0 C. temperatures.
Briefly stated, the foregoing and numerous other features, objects and advantages of the present invention will become readily apparent upon a review of the detailed description, claims and drawings set forth herein. These features, objects and advantages are accomplished by fabricating a thermal actuator for a micro-electromechanical device comprising a base element and a cantilevered element extending from the base element, the cantilevered element normally residing in a first non-actuated position. The cantilevered element includes a first layer constructed of a dielectric material having a low thermal coefficient of expansion and a second layer of intermetallic titanium aluminide (Ti/Al) attached to the first layer. A pair of electrodes are connected to the second layer to allow an electrical current to be passed through the second layer to thereby cause the temperature of the second layer to rise. The heat generated as a result of the resistivity of the intermetallic titanium aluminide causes the cantilevered element to deflect to an actuated second position. The cantilevered element returns to the first position when the electrical current through the second layer is ceased and the temperature of the second layer decreases. The intermetallic titanium aluminide thin film comprising the second layer has a high coefficient of thermal expansion and is electrically conductive. Further, the intermetallic titanium aluminide thin film has suitable resistivity for use as a heater. With selected deposition conditions and post deposition annealing, a film with properly adjusted stress and thermal stability is formed.
The present invention is particularly useful as a thermal actuator inkjet printer device. In this preferred embodiment, the cantilevered element of the thermal actuator resides in an ink reservoir or chamber that includes a port or nozzle through which ink can be ejected. Through actuation of the thermal actuator, the cantilevered element deflects into the chamber forcing ink through the nozzle.
As stated above, the cantilevered element includes a first layer constructed of a dielectric material having a low thermal coefficient of expansion. The term xe2x80x9clow thermal coefficient of expansionxe2x80x9d as used herein is intended to mean a thermal coefficient of expansion that is less than or equal to 1 ppm/xc2x0 C.